An electric arc furnace (EAF) is a furnace utilizing electric arc to melt metal or metal alloys. A typical EAF comprises three electrodes, a power supply system operatively connected to the electrodes and a vessel. The vessel is provided with a refractory lining for withstanding high temperature. The EAF is further equipped with gas burners mounted on the sidewalls and arranged to provide chemical energy to a melt. Additional chemical energy is provided by means, e.g. lances, for injecting oxygen and carbon into the furnace. The operation of the electrodes is controlled by a control unit operatively connected to the power supply system. The power supplied to the electrodes thereby creating an arc is called arc power. The electrodes form an arc between the electrodes and the metallic material, i.e., solid metal (e.g. scrap) that has been loaded into the EAF. Thereby, a metallic melt is created and heated by the arc power and chemical energy from the oxygen injection. An electrode controlling system maintains approximately constant current and power input during the melting of the metallic material.
Both molten metal and melt mean metal in a liquid form.
An electromagnetic stirring (EMS) system may be arranged to stir the melt in the furnace. A typical EMS-system comprises at least one electromagnetic stirrer comprising a stirring coil, a power supply system is operatively connected to the stirrer and including a frequency converter and a transformer, a cooling water station and at least one control unit operatively connected to the power supply system to control the operation of the stirrer. The stirring coil is typically mounted outside a steel shell of the furnace. This coil generates a travelling magnetic field to provide stirring forces to the melt. The stirrer operates at a low frequency travelling magnetic field, penetrating the steel shell of the furnace and moving the melt in a way similar to a linear electric motor. Thus, a linear force is created by the travelling linear magnetic field acting on the melt in the furnace. The power supplied to the electromagnetic stirrer is called stirring power.
The stirring power is often determined by an ad hoc scheme that is largely depending on experiences of an operator at a production site. This means that the operator decides the stirring operation, i.e. the intensity/strength of the stirring, by manually switching on or off the stirring power. The ad hoc scheme not only results in refractory wears of the EAF but also unnecessary electric energy consumption.
WO 2013/010575 discloses a method and a control system for controlling a melting process in an electric arc furnace for melting a metallic material. The method comprises the steps of receiving or collecting measured data of at least one process variable, determining the current state of the process, performing an optimization of the melting process, determining a process input based on the result of the optimization, and controlling the melting process by means of the process input.